What are Tailings and Tailings Storage Facilities. After the desired mineral has been removed from the ore, trash is left behind, known as tailings. They are made up of crushed rock, water and traces of metals including copper, mercury, cadmium, zinc, and others. Tailings are often kept on the surface in structures known as tailings dams or tailings storage facilities after leaving the mine processing plant in a slurry state (diluted with water). Tailings storage facilities (TSF) are engineered buildings that include tailings dams and other works to keep the waste in place. They are made to hold tailings, which are the waste left over after valuable materials are taken out of metal ores, and to control any water that comes with them.